The prospect for the merged business were further clouded on Wednesday as Germany's E.On - which under the spin-off plans would have a 34% stake in the new UK energy firm - said it would have "no strategic interest" in holding onto that stake.

E.On, which already operates one of the big six UK energy suppliers, is in the process of acquiring network and retail assets from German rival Innogy, which currently owns npower.

SSE reported a loss of £68.7m for its household supply arm for the six months to the end of September, up from £17.8m last year.

It blamed lower demand, higher energy costs and the decision not to further raise tariffs. At the same time, customer account numbers fell by 460,000 to 6.48 million.